C golfing tips - returning 0 without return statement

Question

I'm looking for some solution in returning values in main function, I need to shorten my program more, return 0 takes too much characters of my code, I need to return 0, or my code fails. I know that in C there can be no return statement, and then program will use result of last operation - but on which operations I can 'really' shorten my code? At the moment I found brk(0) as shortest return.

main(n){while(~scanf("%i",&n))printf("%i ",n*~n/-2);brk(0);}

Answer 1

You don't need to do anything.

This assumption:

then program will use result of last operation

is erroneous. If there is no return statement, main returns 0. It is not dependent on whatever might be left over in registers or anything like that.

From the standard:

5.1.2.2.3 Program termination

If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument; reaching the } that terminates the main function returns a value of 0. If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

(emphasis mine)

Your program's main already returns zero, or something is wrong somewhere else.

Answer 2

To be precise, the return value is generally dependent not on any previous "operation", but on the return value of the last function call. You are hoping that the function dumps a 0 into the EAX register, and that it stays there when main returns.

You may be able to get better mileage out of atoi/atol and gets here. When gets hits EOF without reading a line, it returns a null pointer. Then, atol will return 0 upon receiving a null pointer as input. Since 0 is not an allowed value for n, this can be used as the loop condition, as well as the way to drop 0 into the appropriate register.

main(n){while(n=atol(gets(??????)))printf("%i ",n*~n/-2);}

The only problem is to find some memory for gets to write on. I'm not familiar with the Unix-specific library functions such as brk, but surely you can find something 6 characters or less (needed for an overall shortening) which returns char* or void* among all the cruft.